Essential Role for Vascular Gelatinase Activity in Relaxin-Induced Renal Vasodilation, Hyperfiltration, and Reduced Myogenic Reactivity of Small Arteries

Abstract

Abstract-During pregnancy, relaxin stimulates nitric oxide (NO)-dependent renal vasodilation, hyperfiltration and reduced myogenic reactivity of small renal arteries via the endothelial ET B receptor subtype. Our objective in this study was to elucidate the mechanisms by which relaxin stimulates the endothelial ET B receptor/NO vasodilatory pathway. Using chronically instrumented conscious rats, we demonstrated that a specific peptide inhibitor of the gelatinases MMP-2 and -9, cyclic CTTHWGFTLC (cyclic CTT), but not the control peptide, STTHWGFTLS (STT), completely reversed renal vasodilation and hyperfiltration in relaxin-treated rats. Comparable findings were observed with a structurally different and well-established, general antagonist of MMPs, GM6001. In contrast, phosphoramidon, an inhibitor of endothelin-converting enzyme, did not significantly change the renal vasodilatory response to relaxin administration. When small renal arteries were incubated with either of the general MMP inhibitors, GM6001 or TIMP-2 (tissue inhibitor of MMP), or with the specific gelatinase inhibitor, cyclic CTT, the reduced myogenic reactivity of these blood vessels from relaxin-treated nonpregnant and midterm pregnant rats was totally abolished. Moreover, a neutralizing antibody specific for MMP-2 completely abrogated the reduced myogenic reactivity of small renal arteries from relaxin-treated nonpregnant and midterm pregnant rats. In contrast, phosphoramidon did not significantly affect the reduction in myogenic reactivity. Using gelatin zymography, we showed increased pro and active MMP-2 activity in small renal arteries from relaxin-treated nonpregnant and midterm pregnant rats relative to the control animals. Thus, inhibitors of MMPs in general and of gelatinases in particular reverse the renal vascular changes induced by pregnancy or relaxin administration to nonpregnant rats. Finally, the typical reduction in myogenic reactivity of small renal arteries from relaxin-treated nonpregnant rats was absent in ET B receptor-deficient rats, despite an increase in vascular MMP-2 activity. These results indicate an essential role for vascular gelatinase, which is in series with, and upstream of, the endothelial ET B receptor/NO signaling pathway in the renal vasodilatory response to relaxin and pregnancy. (Circ Res. 2003;93:1249-1257.)Key Words: nitric oxide Ⅲ endothelin B receptor Ⅲ pregnancy Ⅲ renal circulation Ⅲ matrix metalloproteinases V asodilation of nonreproductive organs is one of the earliest and most dramatic of maternal adaptations to human pregnancy. The gravid rat manifests comparable circulatory changes including renal vasodilation and hyperfiltration. 1,2 Consequently, this animal model has been extensively investigated in order to elucidate the mechanisms underlying the renal vasodilatory response to pregnancy. Endothelin (ET) has been shown to mediate nitric oxide (NO)-dependent renal vasodilation and hyperfiltration during pregnancy, as well as reduced myogenic reactivity of small renal arteries via the ET B rec...

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“…Although the small renal arteries harvested from these rats showed upregulation of vascular MMP-2 activity, they failed to elicit the typical reduction in myogenic reactivity. This observation when taken in the context of the other results (supra vide) indicates that vascular gelatinase is in series with and upstream of the endothelial ET B -NO signaling pathway in the renal vasodilatory response to pregnancy mediated by relaxin (32).…”

“…Jeyabalan et al (32) (Figure 1) recently proposed that relaxin upregulates vascular gelatinase activity during pregnancy, thereby contributing to renal vasodilation, hyperfiltration, and reduced myogenic reactivity of small renal arteries through activation of the endothelial endothelin B (ET B ) receptor-NO pathway. The notion that metalloproteinase 2 (MMP-2) plays a pivotal role in the relaxin-gelatinase pathway is based on the confluence of several observations.…”

“…By inhibiting gelatinase activity in chronically instrumented rats in vivo and in isolated small renal arteries in vitro, Jeyabalan et al (32) demonstrated an essential role for vascular gelatinase in the relaxin-mediated, renal circulatory changes of pregnancy. In contrast, the traditional endothelium-converting enzyme pathway that processes big ET to ET is not involved on the basis of the lack of any hemodynamic effect of the traditional endothelium-converting enzyme inhibitor phosphoramidon.…”

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“…For instance, MMP-2 and MMP-9 can acutely enhance vascular tone through the cleavage of vasoactive peptides such as adrenomedullin, calcitonin gene-related peptide and big endothelin-1 [16,[33][34][35]. Another non-ECM acute action of MMPs and ADAMs is shedding of membrane-anchored ligands of receptors such as epidermal growth factor (EGF) and platelet-derived growth factor (PDGF) to transactivate intracellular signaling of growth via the MAPK cascade.…”

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“…In the spontaneously hypertensive rat vasculature, MMP-2 cleaves vascular VEGFR-2 in cardiac microvessels to mediate endothelial apoptosis and capillary rarefaction which contribute to the development of hypertension [10]. MMP-2 and MMP-9 have also been implicated in cleavage of big ET at a Gly-Leu bond of big ET (ET ) to form a smaller peptide (ET ), which activates the endothelial ET B /NO vasodilatory pathway and could thus mediate the vascular effects of the pregnancy hormone, relaxin [37]. In addition MMP-2, but not MMP-9, has been proposed to cleave the vasodilator peptide adrenomedullin, which adds yet another pathway by which MMP-2 could regulate systolic blood pressure [38].…”